A new app can detect whether you have AFib. Patric Sandri/IKON Images/Getty Images

Watches used to simply tell the time. Now, the smart variety can track steps taken, sleep habits and even whether or not you have a type of irregular heart rhythm known as atrial fibrillation (AFib). In fact, AFib can be detected with about 97 percent accuracy using an app called Cardiogram in conjunction with a smart watch, like the Apple Watch.

These findings come courtesy of the Health eHeart study, and were presented by Dr. Greg Marcus with the University of California, San Francisco at the Heart Rhythm Society Annual Scientific Session. "The idea was to use the technology that is now ubiquitously available," explains Marcus, director of clinical research for the division of cardiology at UCSF.

AFib is the most common form of heart arrhythmia, and affects an estimated 2.7 to 6.1 million people in the United States alone, either on a permanent or temporary basis. It is characterized by irregular beating in the upper chambers of the heart, causing the blood to not flow as well as it should.

Smart watches accomplish the impressive feat of identifying AFib using a sensor to detect the pulse. "Essentially it shines a light and it looks at changes in skin tone that reflect a pulse," Dr. Marcus says. "Every time there's a pulse, the color of the skin changes just a little bit but enough for a gadget to detect." This variation tips off the sensor that something could be amiss.

The process wasn't as simple as testing an app, however. UCSF partnered with Cardiogram to train the app's algorithm to identify when a person experiences AFib with the help of many patients with known AFib. After the algorithm had been "taught" to recognize AFib, they moved onto the next phase.

"Once we had the algorithm trained we tested it on people with documented AFib where we shock the heart back to the normal rhythm," explains Dr. Marcus. Although most were shocked back into normal rhythm, some were converted using medication. "We fitted them with the Apple watch with the app downloaded. Then, we used the app during AFib and subsequently during normal rhythm. So, we saw both rhythms in the same person."

Determining whether a person is experiencing AFib is trickier than it sounds, so the development of the app as a screening tool is a welcome addition to the diagnostic process. "A classic characteristic of atrial fibrillation is that the heart rate or rhythm is irregularly irregular. There is no pattern, it's completely random," Dr. Marcus says. In fact, if a person wears a heart monitor long enough he's likely to experience some sort of irregular rhythm eventually.

AFib often lurks silently. Many people have mild, if any symptoms. Those who do report a sensation of irregular heartbeat (palpitations), feeling out of breath, fatigued or faint. Although it can pose a serious threat in terms of stroke risk, AFib can be controlled by medication, so it's best to pinpoint it as early as possible. Anyone can use the app, but the most likely to benefit are people with risk factors, like high blood pressure, heart failure, diabetes, coronary artery disease and previous history of stroke, as well as being over age 60.

Scary thought it might sound, AFib isn't an imminently life-threatening rhythm. Instead, doctors want to identify it to reduce stroke risk over the very long term. "For the great majority of individual public with heart palpitations they are usually not anything dangerous or life-threatening. The primary purpose of evaluation and treatment is to help with quality of life," Marcus says.

However, don't think you can use the app to diagnose AFib on its own. "We need to roll it out in a useful way that minimizes false positives, Dr. Marcus says. "I don't think this is going to be sufficient to diagnose AFib, but rather would be a way to identify potential AFib. But once in use, it would require confirmation using an EKG."

The Cardiogram app and its capabilities join a wave of similar devices designed to identify looming health crises, such as bathroom scales that can detect cardiac arrhythmia or arteriosclerosis.

Now That's Cool

The Health eHeart study enrolls people on an ongoing basis to contribute data to help fight heart disease. More than 100,000 people have registered, but the researchers are hoping to reach the 1 million mark. (Participants primarily fill out quick online surveys about their sleep habits, medical conditions, etc).